Furnace



G. H. HOWE FURNACE Original Filed Sept. 17, 1937 Inyentor:

h :OWe, by is Attorney GOOdWI S i m Patented Apr. 16, 1940 PATENT OFFICE FURNACE Goodwin H. Howe, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Original application September 17, 1937, Serial 164,354. Divided and this application January 3, 1938, Serial No. 183,146

4 Claims.

This application is a division of my copendlng application Serial No. 164,354, Sintered alloy and netqhod for making the same, filed September 1'7, 1 3

The present invention relates to a furnace structure and more particularly to a furnace adapted to be employed in the fabrication of sintered alloys having the composition disclosed in Ruder Patents 1,947,274 and 1,968,569 and Mishima Patents 2,027,994 to 2,028,000 inclusive. In the fabrication of alloys from mixed, pressed, powdered ingredients as disclosed in my prior application, it is desirable to employ a hydrogen or other suitable reducing atmosphere of the highest degree of purity whereby oxidation of the ingredients may be avoided.

It is one of the objects of the present inven tion to provide a hydrogen furnace in which the hydrogen atmosphere is purified to an unusually high degree and in which the sintering of the alloy and subsequent production of a precipitation condition in the alloy may be effected in a single passage through the furnace. Further objects will appear hereinafter.

The novel features which are characteristic of my invention will be set forth with particularity in the appended claims. The invention itself, however, will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which Fig. 1 is a view in elevation of a hydrogen furnace which may be employed in carrying my invention into effect; Fig. 2 is a longitudinal sectional view, broken away and on an enlarged scale, of the apparatus disclosed in Fig. 1; Fig. 3 is an end view of the furnace shown in Fig. 2, while Fig. 4 is a perspective view of a boat employed in the operation of the furnace and adapted to hold and convey the material to be sintered through the furnace.

In carrying out my invention, I employ a furpace I which comprises the usual heating chamber 2, supplied with hydrogen gas through a pipe 0. An elongated, rectangular, steel tube 4, which extends through and beyond each end of the heating chamber of furnace l, comprises a heating or sintering chamber 5 coextensive with the heating chamber 2, and a cooling chamber 6 which is an extension of the sintering chamber 5.

0 The inlet and outlet ends of tube 4 are provided with doors or closure members I and 8 respectively. Outlet door 8 is provided with an opening 9 which in the present case is about .040" in diameter, while the inlet door I is provided with a 56 larger opening '0 about .052" in diameter.

Slotted pipes II and I2, positioned beneath these doors, supply a curtain of hydrogen over the ends of the tube 4 and prevent access of air, particularly by convection, to the interior of the tube when either door is opened. The portion of the tube 4 comprising the cooling chamber 6 is cooled by a water jacket I3, having an inlet pipe l4 and an outlet pipe l5 for the circulation of a cooling medium therethrough.

In operation the tube 4 is heated to a temperature above 1000" C. and preferably at abou 1400 C. by means of the usual heater coil l6. Hydrogen, which preferably, although not necessarily, has been purified and dried to remove moisture therefrom, is supplied to the tube at a point between the heating and cooling zones through a pipe 11. As the hydrogen enters tube 4 it divides. One part flows towards the outlet opening 9, while the remainder and greater portion flows towards and out of the larger opening In in the closure member 1. Ordinary line hydrogen may be supplied to the heating zone 2 of the furnace I through pipe 3. This hydrogen is burned as it emerges from the opening [8, while the hydrogen in tube 4 is burned as it emerges from openings 9 and ill. The pieces of material Hi to be sintered are positioned on metal boats 20 which are pushed slowly through tube 4 by means of a rod 2| operated by a driving device 22.

That portion of the hydrogen in tube 4 which flows towards the opening l0 comes in contact with the sintered pieces emerging from the hottest zone in the furnace. At this temperature, about 1400 C., the hydrogen is purified to a very high degree, substantially all trace of oxygen being removed therefrom. No reaction to form water takes place, however, as the surface of the sintered material, in this case, permanent magnet material containing as essential ingredients, iron, nickel, and aluminum, is practically inert to reduction after oxidation, due to the aluminum content of the alloy. When the purified hydrogen reaches the point where the presssed material I9 enters the heating zone of the tube 2, it has attained an unusually high degree of purity and protects the pressed material against oxidation and also reduces any trace of oxide on the pressed pieces iii.

In a 4" furnace of the type disclosed and having outlets as designated, the magnetic properties of sintered alloy are progressively improved as the hydrogen flow is increased from about 4 to 10 cubic feet per hour. Although freshly hydrogen cleaned, powdered materials are employed in fabricating the alloys, some degree of oxidation of the powdered materials occurs during mixing and pressing. However, since the relatively large hydrogen discharge opening is at the inlet end of the tube 4. the hydrogen flow is in the proper direction to maintain an extremely high degree of purity at the inlet point of tube 4 where the demand is most critical.

The time required for a boat 20 to pass through the heating zone in the tube 4 usually varies from about one-half to two hours depending upon the size of the pieces to be sintered. The temperature of the hot zone grades off from about 1400 C. at the center to about 1050 C. to 1150 C. at the end adjoining the cooling chamber. As a boat approaches the end of the hot zone 5 the outlet door 8 is opened and the operator inserts a rod and pulls the boat quickly into the cooling chamber 8, where the sintered material is permitted to cool below 600 C. The cooling period usually varies from about 10 to about 30 minutes according to the composition, size of pieces l9, and magnetic properties desired. The cooling rate may be controlled by varying the rate of flow of the cooling medium in water jacket l3.

The material carried on the fore-end of the first boat load which is passed through the sintering chamber may under some conditions be oxidized. To avoid any spoilage of good material, it is advisable to push through the tube 4, a preliminary load of scrap material which will serve to clean up the hydrogen in preparation for succeeding loads.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A furnace comprising a heating'chamber, a

tube supported in and extending through said,

chamber and adapted to contain material to be heat treated, said tube having inlet and outlet closure members at opposite ends thereof, means for cooling 9. portion of said tube adjacent the outlet end thereof, means for supplying a reducing gas to said chamber, means for supplying a reducing gas to said tube at a point between said cooled portion and said heating chamber, means for effecting a flow of said reducing gas in opposite directions in said tube and means for controlling the flow of reducing gas in each of said directions.

2. A furnace comprising a heating chamber, a tube supported in and extending through said chamber and adapted to contain material to be heat treated, said tube having inlet and outlet closure members at opposite ends thereof, means for cooling 9. portion of said tube adjacent the outlet end thereof, means for supplying a reducing gas to said chamber, means for supplying a reducing gas to said tube'at a point between said cooled portion and said heating chamber, means for effecting a flow of said reducing gas in opposite directions in said tube, and means associated with said closure members for controlling the flow of gas toward the inlet and outlet ends of said tube.

3. A furnace comprising a heating chamber, a tube extending through said chamber and adapted to contain material to be heat treated said tube having inlet and outlet closure members at opposite ends thereof, each of said closure members having a small opening therethrough, the opening in one of the closure members being larger than the opening in the other closure member, means for cooling a portion of said tube adiacent said outlet closure member, means for supplying hydrogen gas to said heating chamber, and means for supplying hydrogen gas to said tube at a point between said cooled portion and said heating chamber.

4. A furnace comprising a heating chamber, a tube supported in and extending through said chamber and adapted to contain material to be heat treated, said tube having inlet and outlet closure members at opposite ends thereof, means for cooling a portion of said tube adjacent the outlet end thereof, means for supplying a reducing gas to said chamber, means for supplying a reducing gas to said tube at a point between said cooled portion and said heated chamber, means for effecting a flow of said reducing gas in opposite directions in said tube, means for controlling the flow of reducing gas in, each of said directions, and means for supplying a curtain of hydrogen over the ends of said tubes when said closure members are opened.

GOODWm H. HOWE. 

